Transcript Atomic Mass - Mayfield High School

Atomic Mass
Atomic Mass
• The weighted average of all natural occurring
isotopes of that element
• Example: Lithium = 6.941 amu
• Atomic number closest to 7, therefore most
isotopes of lithium of a mass number of 7
• Rubidium has two common isotopes, 85Rb
and 87Rb. If the abundance of
• 85Rb is 72.2% and the abundance of 87Rb is
27.8%, what is the average
• atomic mass of rubidium?
.722 x 85
(%) times (mass number)
+
.278 x 87
(%) times (mass number)
=
85.55